1. Field of the Invention
This invention is related to a luminescent material, a manufacturing method of the luminescent material, and light-emitting device.
2. Description of the Related Art
A light-emitting diode (LED) is constituted of a combination of an LED chip as a light source for excitation and a luminescent material, and various colors can be emitted by that combination. In a white LED emitting white light, a combination of LED chips emitting light having a wavelength ranging from 360 nm to 500 nm and luminescent materials is used. For instance, a combination of the LED chips emitting light of mainly blue region and yellow luminescent material which emits luminescence of yellow color can be mentioned. Furthermore, a combination of the LED chips emitting light of ultraviolet or near-ultraviolet ray region and luminescent material mixture can be mentioned. In the luminescent material mixture, a blue luminescent material which emits luminescence of blue color, a green-yellow luminescent material which emits luminescence of green-yellow color, and red luminescent material which emits luminescence of red color are contained. As for the luminescent material used for the white LED, it is demanded that the luminescent material absorbs light in the region from the near-ultraviolet region to the blue region of light-emitting wavelength of 360 to 500 nm well, and that efficiently emits visible light.
White LEDs using alkaline earth ortho-silicate luminescent material activated by bivalent europium are proposed. Such a luminescent material has a composition represented by (Sr,Ba,Ca)2SiO4:Eu and capable of emit a light having arbitrary peak wavelength by varying mixing ratio of alkaline earth metal element. However, these white LEDs are used by combination with luminescent material having broadband emission spectrum of half-width 80 nm or more. For that reason, there is a limit in color rendering property.
Furthermore, the white LEDs in which luminescent material activated by Tb and light-emitting element have been proposed. The light-emitting element used here is that which has the light emission peak at 365 nm. The 365 nm ultraviolet LED has too much short wavelength for illumination use, and degradation of resin coating the luminescent material is large. Furthermore, manufacturing cost of the 365 nm ultraviolet LED is higher than that of the LED chip which emits light in 370-460 nm region, and conversion efficiency from electricity to light is low.